Patent application title: FUEL CELL STACK AND FUEL CELL USING THE SAME

Abstract:

A fuel cell stack of the present invention includes: a membrane electrode
assembly, formed by stacking an anode electrode, a cathode electrode, and
an electrolyte membrane interposed between the anode electrode and the
cathode electrode; and a sealing structure for preventing a fuel that is
supplied to the anode electrode and a gas containing an oxidizer that is
supplied to the cathode electrode from leaking in a direction different
from a stacking direction of the membrane electrode assembly, and has a
configuration where pressing force of the sealing structure on the anode
electrode side is set larger than pressing force on the cathode electrode
side. There are provided a fuel cell stack having a sealing structure
excellent in assembly property and replacement property, and a fuel cell
using the same.

Claims:

1. A fuel cell stack, comprising: a membrane electrode assembly, formed
by stacking an anode electrode, a cathode electrode, and an electrolyte
membrane interposed between the anode electrode and the cathode
electrode; an anode-side end plate; a cathode-side end plate; and a
sealing member, provided between the anode-side end plate and the
cathode-side end plate, wherein the membrane electrode assembly is
sandwiched by the anode-side end plate and the cathode-side end plate
from both sides of the stacking direction of the membrane electrode
assembly, the electrolyte membrane has a protruding section exposed from
the anode electrode and the cathode electrode, the sealing member is at
least provided with a ringed substrate that makes the anode electrode and
the cathode electrode present inside, and a ringed elastic body formed on
the substrate, the elastic body compresses by pressing the protruding
section onto the anode-side end plate, while pressing the substrate onto
the cathode-side end plate, thereby to form a sealing structure for
preventing a fuel that is supplied to the anode electrode and a gas
containing an oxidant that is supplied to the cathode electrode from
leaking in a direction different from a stacking direction of the
membrane electrode assembly, and pressing force of the sealing structure
on the anode electrode side is set larger than pressing force on the
cathode electrode side.

2. (canceled)

3. The fuel cell stack according to claim 1, wherein a grooved gas flow
channel for circulating the gas is provided on a surface of the
cathode-side end plate which is opposed to the cathode electrode, while
reaching a side surface of the cathode-side end plate, and the substrate
has sufficient strength for compressing the elastic body at a portion
crossing over the gas flow channel.

4. The fuel cell stack according to claim 1, wherein an area of the
elastic body which is in contact with the protruding section is smaller
than an area of the elastic body which is in close contact with the
substrate.

5. A fuel cell stack comprising two membrane electrode assemblies, each
formed by stacking an anode electrode, a cathode electrode, and an
electrolyte membrane interposed between the anode electrode and the
cathode electrode, the stack comprising: a separator, provided between
the membrane electrode assemblies; an anode-side end plate; a
cathode-side end plate; a first sealing member, provided between the
separator and the anode-side end plate; and a second sealing member,
provided between the separator and the cathode-side end plate, wherein
two of the membrane electrode assemblies are sandwiched by the anode-side
end plate and the cathode-side end plate from both sides of the stacking
direction of the membrane electrode assembly, the electrolyte membrane
has a protruding section exposed from the anode electrode and the cathode
electrode, the first sealing member is provided with a ringed first
substrate and a ringed first elastic body formed on the first substrate,
and the first elastic body compresses by pressing the protruding section
onto the anode-side end plate, while pressing the first substrate onto
the separator, the second sealing member is provided with a ringed second
substrate and a ringed second elastic body formed on the second
substrate, and the second elastic body compresses so as to press the
protruding section onto the separator, while pressing the second
substrate onto the cathode-side end plate, and the protruding section of
the electrolyte membrane, the first sealing member and the second sealing
member constitute a sealing structure for preventing a fuel that is
supplied to the anode electrode and a gas containing an oxidant that is
supplied to the cathode electrode from leaking in a direction different
from a stacking direction of the membrane electrode assembly, and
pressing force of the sealing structure on the anode electrode side is
set larger than pressing force on the cathode electrode side.

6. The fuel cell stack according to claim 5, wherein grooved gas flow
channels for circulating the gas are provided respectively on the
cathode-side end plate and a surface of the separator which is opposed to
the cathode electrode, while reaching side surfaces of the cathode-side
end plate and the separator, and the first substrate and the second
substrate have sufficient strength for compressing the first elastic body
and the second elastic body at portions crossing over the gas flow
channels.

7. The fuel cell stack according to claim 5, wherein areas of the first
elastic body and the second elastic body which are in contact with the
protruding section of the electrolyte membrane are smaller than areas of
the first elastic body and the second elastic body which are in close
contact with the first substrate and the second substrate.

8. A fuel cell stack comprising three or more membrane electrode
assemblies, each formed by stacking an anode electrode, a cathode
electrode, and an electrolyte membrane interposed between the anode
electrode and the cathode electrode, the stack comprising: a separator,
provided between the membrane electrode assemblies; an anode-side end
plate; a cathode-side end plate; a first sealing member, provided between
the separator and the anode-side end plate; and a second sealing member,
provided between the separator and the cathode-side end plate a third
sealing member, provided between the separator arranged on an anode side
and the separator arranged on a cathode side among the separators,
wherein the third sealing member is provided with a ringed third
substrate and a ringed third elastic body formed on the third substrate,
and the third elastic body is compressed by pressing the protruding
section onto the separator arranged on the anode side, while pressing the
third substrate onto the separator arranged on the cathode side, and the
protruding section of the electrolyte membrane, the first sealing member,
the second sealing member and the third sealing member constitute a
sealing structure for preventing a fuel that is supplied to the anode
electrode and a gas containing an oxidant that is supplied to the cathode
electrode from leaking in a direction different from a stacking direction
of the membrane electrode assembly, and pressing force of the sealing
structure on the anode electrode side is set larger than pressing force
on the cathode electrode side.

9. The fuel cell stack according to claim 8, wherein grooved gas flow
channels for circulating the gas are provided on the cathode-side end
plate and a surface of the separator which is opposed to the cathode
electrode, while reaching side surfaces of the cathode-side end plate and
the separator, and the first substrate, the second substrate and the
third substrate have sufficient strength for compressing the first
elastic body, the second elastic body and the third elastic body at
portions crossing over the gas flow channels.

10. The fuel cell stack according to claim 8, wherein areas of the first
elastic body, the second elastic body and the third elastic body which
are in contact with the protruding section of the electrolyte membrane
are smaller than areas of the first elastic body, the second elastic body
and the third elastic body which are in close contact with the first
substrate, the second substrate and the third substrate.

11. A fuel cell, comprising: a fuel cell stack according to claim 1; a
fuel supply section that supplies an anode electrode with a fuel; and an
oxidant supply section that supplies a cathode electrode with an
oxidizer.

Description:

RELATED APPLICATIONS

[0001] This application is the U.S. National Phase under 35 U.S.C.
§371 of International Application No. PCT/JP2009/003736, filed on
Aug. 5, 2009, which in turn claims the benefit of Japanese Application
No. 2008-203983, filed on Aug. 7, 2008, the disclosures of which
Applications are incorporated by reference herein.

TECHNICAL FIELD

[0002] The present invention relates to a fuel cell stack and a fuel cell
using the same, and particularly relates to a sealing structure of a fuel
cell stack.

BACKGROUND ART

[0003] In recent years, electronic equipment are rapidly becoming more
portable and cordless, and there is an increasing demand for secondary
batteries which are smaller in size and lighter in weight and have higher
energy densities, as power sources for driving those equipment. Further,
not only application of small consumer batteries, but also technology
development on large secondary batteries required to have long-lasting
durability and safety, such as those for power storage or an electric
vehicle, has been accelerated. Moreover, a fuel cell continuously usable
for a long period of time by supply of a fuel has received more attention
than the secondary battery that needs charging.

[0004] The fuel cell at least has a fuel cell stack including a cell
stack, a fuel supply section that supplies a fuel to the cell stack, and
an oxidant supply section that supplies an oxidant. Generally, a
separator and a membrane electrode assembly, which is made up of an anode
electrode, a cathode electrode and an electrolyte membrane interposed
between those electrodes, are stacked and end plates are provided on both
ends of the stacking direction, to constitute the cell stack. Therefore,
the cell stack requires mutually close stacking of the anode electrode,
the cathode electrode and the electrolyte membrane. This is not only for
bringing about an equivalent electrochemical reaction, but also for
preventing leakage of the fuel and oxygen (air) as the oxidant from
between the end plate/the separator and the anode electrode/the cathode
electrode due to grooves for circulating the fuel and oxygen which are
provided on the end plates and the separator.

[0005] In order to realize this, there is disclosed a gasket with a
structure where a convex lip held on one separator and a convex lip held
on the other separator are combined to seal an electrolyte membrane from
both sides (e.g. refer to Patent Document 1). However, in the sealing
structure of Patent Document 1, the opposing one convex lip cannot be
provided in a fuel or oxidant gas flow channel. Hence, with only one
convex lip provided, gas leakage or the like may occur due to shortage of
sealing surface pressure.

[0006] There is then disclosed an example of a structure where, in an area
formed with a gas channel or the like that prevents combination of a flat
lip held in one separator and a convex lip held in the other separator, a
tongue-like projecting section is provided on the periphery of a gas
diffusion layer in a membrane electrode assembly and the convex lip or
the flat lip and the projecting section are combined, to seal the
electrolyte membrane from both sides (e.g. refer to Patent Document 2).
However, also in Patent Document 2, with only the flat lip provided on
the other separator, an area sealed by combination of the flat lip and
the projecting section is generated. Resultantly, due to a wide contact
area with the flat lip, high sealing surface pressure may not be
obtained, and hence reliable sealing performance cannot be realized.

[0007] For solving the above, there is disclosed a gasket for a fuel cell
with a structure where a second seal is further provided in an area
having the flat lip and the projecting section in combination in the
sealing structure of Patent Document 2, to certainly perform sealing by
combination of the flat lip and the convex lip or the convex lip and the
projecting section (e.g. refer to Patent Document 3). This can improve
the sealing surface pressure, to ensure high sealing property.

[0008] However, in the sealing structure of the fuel cell stack shown in
Patent Document 3, the separator is integrally molded with the convex lip
or the flat lip and sealing is performed from both sides of the
electrolyte membrane in the membrane electrode assembly, thereby
requiring high molding accuracy and positioning accuracy. Similarly,
since the fuel and the oxidant are supplied to each cell through
manifolds, the periphery of the manifold needs sealing as well as the
periphery of the membrane electrode assembly. This requires the convex
lip or the flat lip to have high flatness accuracy and uniform
pressurization for preventing deterioration in sealing property due to
warpage or the like. Consequently, the productivity and assembly
efficiency are degraded.

[0009] Further, in the case of the integrally molded separator being
defective, the separator itself needs replacing, thus making it difficult
to lower cost. Moreover, with the double sealing structure formed, a
large area is required for sealing. This results in a limited area of a
power generating section, and when the area of the power generating
section increases, it becomes difficult to reduce the fuel cell stack in
size.

[0015] The present invention provides a fuel cell stack having a sealing
structure excellent in assembly property and replacement property, and a
fuel cell using the same. A fuel cell stack of the present invention
includes: a membrane electrode assembly, formed by stacking an anode
electrode, a cathode electrode, and an electrolyte membrane interposed
between the anode electrode and the cathode electrode; and a sealing
structure for preventing a fuel that is supplied to the anode electrode
and a gas containing an oxidant that is supplied to the cathode electrode
from leaking in a direction different from a stacking direction of the
membrane electrode assembly. Pressing force of the sealing structure on
the anode electrode side is set larger than pressing force on the cathode
electrode side. The sealing structure is made up of the sealing member
which is at least provided with a ringed substrate that makes the anode
electrode and the cathode electrode present inside, and a ringed elastic
body formed on the substrate.

[0016] It is thereby possible to reliably seal leakage of the fuel from
the anode electrode side by high pressing force of the sealing structure.
Further, it is possible to realize a fuel cell stack, in which the
substrate prevents displacement associated with deformation of the
elastic body and which is easy to assemble and replace owing to the
substrate that can be processed with high accuracy and has high shape
stability.

[0017] According to the present invention, it is possible to realize with
a simple configuration a fuel cell stack having high positioning
accuracy, excellent sealing property and high production efficiency, and
a fuel cell using the same.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a block diagram showing a configuration of a fuel cell in
Embodiment 1 of the present invention.

[0019]FIG. 2 is a sectional schematic view explaining a power generating
operation of the fuel cell in Embodiment 1 of the present invention.

[0020]FIG. 3A is an exploded perspective view of a fuel cell stack in
Embodiment 1 of the present invention.

[0043]FIG. 11 is a sectional view explaining a structure of a fuel cell
stack in Embodiment 3 of the present invention.

[0044]FIG. 12A is a perspective view showing a structure of another
example of a fuel cell in Embodiment 3 of the present invention.

[0045] FIG. 12B is a sectional view taken along line 12B-12B of FIG. 12A.

PREFERRED EMBODIMENTS FOR CARRYING OUT OF THE INVENTION

[0046] Embodiments of the present invention are described hereinafter with
reference to drawings by taking a direct methanol fuel cell (DMFC) as an
example. It is to be noted that the present invention is not restricted
to descriptions given below so long as being based upon basic
characteristics described in the specification.

Embodiment 1

[0047]FIG. 1 is a block diagram showing a configuration of a fuel cell in
Embodiment 1 of the present invention. FIG. 2 is a sectional schematic
view explaining a power generating operation of the fuel cell in
Embodiment 1 of the present invention. A brief summary and an operation
of the fuel cell are described hereinafter with reference to FIGS. 1 and
2.

[0048] As shown in FIG. 1, the fuel cell at least has fuel cell stack 1,
fuel tank 4, fuel pump 5, air pump 6, control section 7, storage section
8 and DC/DC converter 9. Further, fuel cell stack 1 has a power
generating section, and generated power is outputted from positive
terminal 2 and negative terminal 3. The outputted power is then inputted
into DC/DC converter 9. At this time, fuel pump 5 supplies anode
electrode 11 of fuel cell stack 1 with a fuel in fuel tank 4. Air pump 6
supplies cathode electrode 12 of fuel cell stack 1 with a gas such as air
as an oxidant. Further, control section 7 controls drives of fuel pump 5
and air pump 6. Moreover, control section 7 controls DC/DC converter 9 to
control an output to external equipment (not shown) and
charging/discharging of storage section 8. Fuel tank 4, fuel pump 5 and
control section 7 constitute a fuel supply section that supplies the fuel
to anode electrode 11 inside fuel cell stack 1. Meanwhile, air pump 6 and
control section 7 constitute an oxidant supply section that supplies the
gas such as the oxidant to cathode electrode 12 inside fuel cell stack 1.

[0049] Hereinafter, a structure and an operation of fuel cell stack 1 are
briefly described. As shown in FIG. 2, fuel cell stack 1 has membrane
electrode assembly (MEA) 14 as a power generating section, and anode-side
end plate 15 and cathode-side end plate 16 which are arranged so as to
sandwich MEA 14. It is to be noted that in the case of the fuel cell
stack being configured by stacking of a plurality of MEAs 14, a separator
is provided between MEAs 14, and MEAs 14 are stacked with the separator
interposed therebetween. MEA 14 is then sandwiched by anode-side end
plate 15 and cathode-side end plate 16 from both end sides of the
stacking direction of MEAs 14.

[0051] Diffusion layers 11A, 12A are made up, for example, of carbon
paper, carbon felt, carbon cloth, or the like. MPLs 11B, 12B are made up,
for example, of polytetrafluoroethylene or
tetrafluoroethylene-hexafluoropropylene copolymer and carbon. Catalyst
layers 11C, 12C are each formed in such a manner that a catalyst
appropriate for each electrode reaction, such as platinum or ruthenium,
is subjected to high dispersion on a carbon surface to form catalyst
bodies, and the catalyst bodies are then bound by a binder. Further,
electrolyte membrane 13 is made up of an ion-exchange membrane that
transmits a hydrogen ion, such as perfluorosulfonate-tetrafluoroethylene
copolymer. Anode-side end plate 15, cathode-side end plate 16 and the
separator are made up, for example, of a carbon material or stainless
steel. Fuel flow channel 15A that circulates the fuel is provided on
anode electrode 11 and gas flow channel 16A that circulates the gas such
as the oxidant is provided on cathode electrode 12, for example in groove
shape or the like.

[0052] In fuel cell stack 1 configured as thus described, in FIGS. 1 and
2, an aqueous solution containing methanol as the fuel is supplied to
anode electrode 11 by fuel pump 5. The gas such as the air as the oxidant
pressurized by air pump 6 is supplied to cathode electrode 12. The
methanol aqueous solution supplied to anode electrode 11 and methanol as
well as water vapor derived from this aqueous solution are diffused all
over MPL 11B in diffusion layer 11A and further pass through MPL 11B, to
reach catalyst layer 11C. Similarly, oxygen contained in the air supplied
to cathode electrode 12 is diffused all over MPL 12B in diffusion layer
12A and passes through MPL 12B, to reach catalyst layer 12C. Methanol
having reached catalyst layer 11C reacts as in Formula 1, and oxygen
having reached catalyst layer 12C reacts as in Formula 2.

CH3OH+H2O→CO2+6H++6e.sup.- Formula 1

3/2O2+6H++6e-3H2O Formula 2

[0053] Consequently, power is generated along with production of carbon
dioxide on anode electrode 11 side and water on cathode electrode 12 side
respectively as reaction products. Carbon dioxide is then discharged to
the outside of the fuel cell. Similarly, a gas not reacting in cathode
electrode 12, such as nitrogen, and unreacted oxygen are also discharged
to the outside of the fuel cell. At this time, since all of methanol in
the methanol aqueous solution does not react on anode electrode 11 side,
as shown in FIG. 1, the discharged methanol aqueous solution is returned
to fuel pump 5 (arrow A). Further, since water is consumed in the
reaction of anode electrode 11, as shown in FIG. 1, water generated in
cathode electrode 12 may be returned to anode electrode 11 side (arrow
B).

[0054] The structure of the fuel cell stack in Embodiment 1 of the present
invention, and especially the sealing structure as a point of the present
invention, are detailed hereinafter with reference to FIGS. 3A to 8D.

[0055]FIG. 3A is an exploded perspective view of the fuel cell stack in
Embodiment 1 of the present invention. FIG. 3B is a sectional view taken
along line 3B-3B of FIG. 3A. At this time, FIG. 3B shows each
constitutional element of FIG. 3A by means of a sectional view of an
integrated fuel cell stack.

[0057]FIG. 4A is a plan view of the membrane electrode assembly, and FIG.
4B is a sectional view taken along line 4B-4B of FIG. 4A. FIG. 5A is a
plan view of the sealing member, and FIG. 5B is a sectional view taken
along line 5B-5B of FIG. 5A. FIG. 6A is a plan view of the anode-side end
plate, FIG. 6B is a sectional view taken along line 6B-6B of FIG. 6A,
FIG. 6c is a sectional view taken along line 6C-6C of FIG. 6A, and FIG.
6D is a sectional view taken along line 6D-6D of FIG. 6A. FIG. 7A is a
plan view of the cathode-side end plate, FIG. 7B is a sectional view
taken along line 7B-7B of FIG. 7A, FIG. 7c is a sectional view taken
along line 7C-7C of FIG. 7A, and FIG. 7D is a sectional view taken along
line 7D-7D of FIG. 7A. FIG. 8A is a plan view explaining a state of the
cathode-side end plate and the sealing member being mounted, FIG. 8B is a
sectional view taken along line 8B-8B of FIG. 8A, FIG. 8C is a sectional
view taken along line 8C-8C of FIG. 8A, and FIG. 8D is a sectional view
taken along line 8D-8D of FIG. 8A.

[0058] As shown in FIGS. 3A and 3B, anode-side end plate 40, membrane
electrode assembly 24, sealing member 30 that realizes the sealing
structure and cathode-side end plate 50 are stacked, and integrated
through a fastening member not shown in the figures, to constitute fuel
cell stack 20 of the present embodiment.

[0060] Moreover, as shown in FIGS. 5A and 5B, sealing member 30 is made up
of ringed substrate 34 provided with opening 32, and elastic body 36
formed on one surface of substrate 34 and at least in contact with
protruding section 25 of electrolyte film 24B in membrane electrode
assembly 24. Opening 32 is at least formed larger than the periphery of
anode electrode 24A or cathode electrode 24C. Hence substrate 34 is
structured so as to make anode electrode 24A and cathode electrode 24C
present inside. At this time, as substrate 34, for example, polyethylene
terephthalate (PET), polyethylene naphthalate, polyether nitrile (PEN),
polyimide, or the like can be used. It is of importance that the
mechanical strength of substrate 34 be sufficiently large strength for
compressing elastic body 36 and be sufficiently larger than the pressing
force generated at the time of stacking of fuel cell stack 1. Therefore,
for example in a case of the pressing force being 0.2 MPa, a material
having a Young's modulus not smaller than 1 GPa is particularly
preferred. Therefore, a glass epoxy substrate (FR-4) having a Young's
modulus of the order of 27 GPa, or the like, would be satisfactorily
used. Moreover, as elastic body 36, a material having a Young' modulus,
for example, of 1 MPa to 5 MPa, such as a rubber type resin, is used. In
this case, a material having a Young's modulus substantially equal to or
larger than the Young's modulus of electrolyte film 24B in membrane
electrode assembly 24 is particularly preferred. Specifically used can be
high saturated rubber such as fluorine rubber, ethylene-propylene based
rubber and hydrogenated nitrile rubber, high saturated thermoplastic
elastomer such as hydrogenated styrene-butadiene copolymer and
hydrogenated styrene-isoprene copolymer, and the like. As thus described,
protruding section 25 and sealing member 30 constitute the sealing
structure.

[0061] As shown in FIG. 6A, anode-side end plate 40 is at least provided
with fuel flow channel 42 that circulates the fuel such as methanol in,
for example, the shape of a zig-zag groove on the surface opposed to the
surface of the anode electrode in membrane electrode assembly 24. At this
time, as shown in FIGS. 6B and 6D, a through hole that reaches fuel flow
channel 42 is provided as fuel inlet 44 or fuel outlet 46 of fuel flow
channel 42 on, for example, each of side surfaces in two directions of
anode-side end plate 40.

[0062] Further, as shown in FIG. 7A, cathode-side end plate 50 is at least
provided with gas flow channel 52 that circulates the gas such as the air
to be the oxidant in, for example, the shape of a zig-zag groove on the
surface opposed to the surface of the cathode electrode in membrane
electrode assembly 24, so as to be orthogonal to fuel flow channel 42. At
this time, as shown in FIGS. 7B and 7D, oxidant inlet 54 or oxidant
outlet 56 of gas flow channel 52 is provided such that gas flow channel
52 reaches, for example, each of side surfaces in two directions of
cathode-side end plate 50 while remaining in groove shape. This is
because such a through hole as fuel inlet 44 of anode-side end plate 40
would cause occurrence of pressure loss in the case of injecting the gas
such as the air. For reduction in this pressure loss, it is preferable to
form gas flow channel 52 to the side surface while remaining in the
groove shape.

[0063] Each of the constitutional elements described above is stacked as
shown in FIGS. 3A and 3B so that elastic body 36 of sealing member 30
comes into contact with anode-side end plate 40 with protruding section
25 of electrolyte film 24B in membrane electrode assembly 24 interposed
therebetween. Further, substrate 34 of sealing member 30 comes into
contact with cathode-side end plate 50. In such a manner, fuel cell stack
20 is formed. At this time, with convex elastic body 36 formed on
substrate 34 as sealing member 30, an area in contact with electrolyte
film 24B is smaller than an area in contact with substrate 34. The
pressing force of sealing member 30, which forms the sealing structure,
on the anode electrode side becomes larger than the pressing force on the
cathode electrode side. This leads to compression of electrolyte film 24B
by large pressing force of elastic body 36 in sealing member 30, thus
allowing hermetic sealing with high sealing surface pressure.

[0064] Accordingly, the fuel such as methanol that is supplied to anode
electrode 11, unreacted methanol and carbon dioxide that are generated
after the reaction, and the like can be reliably prevented from leaking
through the contact surface between anode-side end plate 40 and
electrolyte film 24B. Further, displacement associated with
transformation of elastic body 36 due to pressing force can be prevented
by substrate 34.

[0065] Meanwhile, as shown in FIGS. 8B or 8D, the upper surface of the
groove shape in the vicinity of inlet 54 or outlet 56 (area shown with a
circle in FIG. 8A) of gas flow channel 52 formed on cathode-side end
plate 50 is crossed over and sealed by substrate 34 of sealing member 30.
At this time, with the mechanical strength of substrate 34 being
sufficiently larger than the pressing force generated at the time of
stacking of fuel cell stack 1, transformation of substrate 34 toward the
inside of the groove on the gas flow channel by the pressing force is
suppressed. It is thus possible to uniformly ensure cross-sectional areas
of gas flow channel 52, and inlet 54 and outlet 56 which are formed by
substrate 34 and gas flow channel 52. Further, since the pressing force
to compress electrolyte film 24B through elastic body 36 of sealing
member 30 does not decrease even on the groove, it is possible to prevent
deterioration in sealing performance.

[0066] Moreover, since elastic body 36 provided on one side of substrate
34 in sealing member 30 presses electrolyte film 24B, as shown in FIG.
3B, electrolyte film 24B transforms into, for example, S shape to realize
the sealing structure, thereby to form a space on anode electrode 11.
This space then becomes a space where the fuel such as methanol bypasses
without passing along fuel flow channel 42, and it is thereby preferable
to make sealing member 30 shaped to have this space as small as possible.
Meanwhile, in the case of sealing by coming into close contact with
cathode-side end plate 50 through substrate 34, the sealing is performed
by a small pressing force as compared with the pressing force on the
anode electrode side. However, substrate 34 and cathode-side end plate 50
are in close contact with each other on the flat surfaces thereof, making
it possible to sufficiently prevent leakage of the air or the like as the
oxidant that is supplied to cathode electrode 24C. Further, with
progression of power generation, dew condensation of generated water
vapor and moisture enter the interface between substrate 34 and
cathode-side end plate 50, thereby allowing further realization of the
sealing structure through the moisture. It is thereby possible to
efficiently prevent the leakage during power generation.

[0067] As thus described, according to Embodiment 1, it is possible to
realize the sealing structure that prevents the fuel that is supplied to
anode electrode 24A and the gas containing the air or the like as the
oxidant that is supplied to cathode electrode 24C from flowing in the
stacking direction of membrane electrode assembly (MEA) 24 and a
direction different from the stacking direction.

[0068] Further, according to Embodiment 1, it is possible to realize a
reliable sealing structure by means of a simple configuration to compress
and press one side of electrolyte film 24B through sealing member 30 made
up of elastic body 36 formed on the one side of substrate 34. It is
therefore possible to realize a fuel cell stack which simplifies
positioning of each constitutional element, and the like, and is thus
excellent in assembly property.

[0069] Moreover, according to Embodiment 1, sealing member 30 is made up
of substrate 34 with high shape stability, thereby making it unnecessary
to form sealing member 30 integrally with cathode-side end plate 50 or
the like. Consequently, since the fuel cell stack can be formed by
stacking, while mounting, each constitutional element, even when the
constitutional element becomes defective after the assembly, it is
possible to replace the element with ease, so as to produce a fuel cell
stack with high productivity and low cost.

[0070] In addition, in Embodiment 1, the description has been given by
means of the example where sealing member 30, anode-side end plate 40 and
cathode-side end plate 50 are in contact with one another on the flat
surfaces thereof, but this is not restrictive. For example, a
semicircular concave section may be formed in a position of anode-side
end plate 40 which is opposed to elastic body 36 of sealing member 30, or
a concave section to be fitted with substrate 34 of sealing member 30 may
be formed on cathode-side end plate 50. This can further improve sealing
performance and positioning accuracy.

[0071] Further, according to Embodiment 1, the description has been given
by means of the example of mutually orthogonal arrangement of fuel flow
channel 42 and gas flow channel 52, but this is not restrictive. For
example, those channels may be formed in the same direction, or may be
formed so as to be opposed to each other by a predetermined angle. This
can enhance degrees of freedom in design.

[0072] Moreover, according to Embodiment 1, the description has been given
by means of the example where the width of substrate 34 of sealing member
30 is made uniform, this is not restrictive. For example, the area of the
position of substrate 34 which crosses over the groove of gas flow
channel 52 may be made larger. It is thereby possible to further increase
the mechanical strength of substrate 34 and further suppress
transformation due to the pressing force of elastic body 36 in the
position of the groove, so as to improve the sealing performance.

[0073] Furthermore, according to Embodiment 1, the description is given,
illustrating the cross sectional shapes of fuel flow channel 42 and gas
flow channel 52 being in the rectangular shapes, but this is not
restrictive. For example, the cross sectional shape may be a polygonal
shape such as a semicircular, triangle or trapezoidal shape.

[0074] Additionally, according to Embodiment 1, the description has been
given by means of the example where the inlets and the outlets of fuel
flow channel 42 and gas flow channel 52 are provided on the side surfaces
opposed to each other or the side surfaces adjacent to each other, but
this is not restrictive. For example, the inlet and the outlet may be
provided on one side surface, and can be arranged arbitrarily in
accordance with arrangement of the fuel pump and the air pump or
designing of the fuel cell.

[0075] Further, in Embodiment 1, the description has been given by means
of the drawings where two gas flow channels are arranged, but this is not
restrictive, and the gas flow channel can be arbitrarily provided in
accordance with an amount of air needed and the configuration of the fuel
cell stack.

Embodiment 2

[0076] A fuel cell stack according to Embodiment 2 of the present
invention is described hereinafter with reference to FIGS. 9 to 10D.

[0077]FIG. 9 is a sectional view explaining a structure of a fuel cell
stack in Embodiment 2 of the present invention. FIG. 10A is a perspective
plan view explaining a structure of a separator of the fuel cell stack in
Embodiment 2 of the present invention, FIG. 10B is a sectional view taken
along line 10B-10B of FIG. 10A, FIG. 10c is a sectional view taken along
line 10C-10C of FIG. 10A, and FIG. 10D is a sectional view taken along
line 10D-10D of FIG. 10A. Fuel cell stack 60 of Embodiment 2 is different
from fuel cell stack 20 of Embodiment 1 in that two membrane electrode
assemblies are stacked with the separator 80 having a fuel flow channel
and a gas flow channel interposed therebetween.

[0078] Specifically, as shown in FIG. 9, anode-side end plate 40, first
membrane electrode assembly 64, second membrane electrode assembly 65,
separator 80 provided between those two membrane electrode assemblies,
first sealing member 70 and second sealing member 75 that realize a
sealing structure, and cathode-side end plate 50 are stacked, and
integrated through a fastening member not shown in the figure, to
constitute fuel cell stack 60 of the present embodiment.

[0079] Herein, as with membrane electrode assembly 24 of Embodiment 1
shown in FIGS. 4A and 4B, first electrolyte 64B and second electrolyte
65B are sandwiched between first anode electrode 64A and first cathode
electrode 64C and between second anode electrode 65A and second cathode
electrode 65C, to constitute first membrane electrode assembly 64 and
second membrane electrode assembly 65. First electrolyte 64B and second
electrolyte 65B have first protruding section 64D and second protruding
section 65D that are exposed from the peripheries of first anode
electrode 64A and first cathode electrode 64C and the peripheries of
second anode electrode 65A and second cathode electrode 65C.

[0080] Further, as with sealing member 30 in Embodiment 1 shown in FIGS.
5A and 5B, first sealing member 70 is at least made up of ringed first
substrate 72 provided with an opening larger than the periphery of the
first anode electrode or the first cathode electrode, and first elastic
body 74 formed on one surface of first substrate 72 and at least in
contact with first protruding section 64D of first electrolyte 64B in
first membrane electrode assembly 64. Similarly, second sealing member 75
is at least made up of ringed second substrate 76 provided with an
opening larger than the periphery of the second anode electrode 65A or
the second cathode electrode 65C, and second elastic body 78 formed on
one surface of second substrate 76 and at least in contact with second
protruding section 65D of second electrolyte 65B in second membrane
electrode assembly 65. Therefore, first substrate 72 is structured so as
to make first anode electrode 64A and first cathode electrode 64C present
inside. Similarly, second substrate 76 is structured so as to make second
anode electrode 65A and second cathode electrode 65C present inside. The
protruding section and the sealing member constitute the sealing
structure. Further, first membrane electrode assembly 64 and second
membrane electrode assembly 65 are sandwiched by anode-side end plate 40
and cathode-side end plate 50 from both sides of the stacking direction.

[0081] Similarly to Embodiment 1 shown in FIGS. 6A to 6D, anode-side end
plate 40 is at least provided with fuel flow channel 42 that circulates
the fuel such as methanol in, for example, the shape of a zig-zag groove
on the surface opposed to the surface of first anode electrode in first
membrane electrode assembly 64. At this time, as shown in FIGS. 6B and
6D, a through hole (not shown) that reaches fuel flow channel 42 is
provided as the fuel inlet or the fuel outlet of fuel flow channel 42 on,
for example, each of side surfaces in two directions of anode-side end
plate 40.

[0082] Further, similarly to Embodiment 1 shown in FIGS. 7A to 7D,
cathode-side end plate 50 is at least provided with gas flow channel 52
that circulates the gas such as the air to be the oxidant in, for
example, the shape of a zig-zag groove on the surface opposed to the
surface of the second cathode electrode in second membrane electrode
assembly 65, so as to be orthogonal to fuel flow channel 42. At this
time, as shown in FIGS. 7B and 7D, oxidant inlet 54 or oxidant outlet 56
of gas flow channel 52 is provided such that gas flow channel 52 reaches,
for example, each of side surfaces in two directions of cathode-side end
plate 50 while remaining in groove shape.

[0083] As shown in FIGS. 10A to 10D, separator 80, which is provided
between first cathode electrode 64C in first membrane electrode assembly
64 and second anode electrode 65A in second membrane electrode assembly
65, has grooved gas flow channel 82 on one surface, and grooved fuel flow
channel 85 on the other surface. At this time, as shown in FIGS. 10A, 10B
and 10D, oxidant inlet 84 or oxidant outlet 86 of gas flow channel 82 is
provided such that gas flow channel 82 reaches, for example, each of side
surfaces in two directions of one surface of separator 80 while remaining
in groove shape. Similarly, a through hole that reaches fuel flow channel
85 is provided as inlet 86 or outlet 87 of fuel flow channel 85 on, for
example, each of side surfaces in two directions of the other surface of
separator 80. It is to be noted that separator 80 is made up of a carbon
material or stainless steel.

[0084] By stacking of each of the above constitutional elements, as shown
in FIG. 9, first elastic body 74 of first sealing member 70 comes into
contact with anode-side end plate 40 with first protruding section 64D of
first electrolyte 64B in first membrane electrode assembly 64 interposed
therebetween. Further, first substrate 72 of first sealing member 70
comes into contact with the surface of separator 80 which is formed with
gas flow channel 82. Similarly, second elastic body 78 of second sealing
member 75 comes into contact with the surface of separator 80 which is
formed with fuel flow channel 85 with second protruding section 65D of
second electrolyte 65B in second membrane electrode assembly 65
interposed therebetween. Moreover, second substrate 76 of second sealing
member 75 comes into contact with the surface of cathode-side end plate
50 which is formed with gas flow channel 52.

[0085] Fuel cell stack 60 is formed in the above manner. At this time,
first elastic body 74 and second elastic body 78 in convex shape are
formed on first substrate 72 and second substrate 76 as first sealing
member 70 and second sealing member 75. For this reason, areas of first
elastic body 74 and second elastic body 78 which are in contact with
first electrolyte 64B and second electrolyte 65B are smaller than areas
of first elastic body 74 and second elastic body 78 which are in contact
with first substrate 72 and second substrate 76. Therefore, the pressing
force on the anode electrode sides of first sealing member 70 and second
sealing member 75, which form the sealing structures, become larger than
the pressing force on the cathode electrode sides. This leads to
compression of first electrolyte 64B and second electrolyte 65B by large
pressing force of first sealing member 70 and second sealing member 75,
thus allowing hermetic sealing on the anode electrode side with high
sealing surface pressure.

[0086] Accordingly, the fuel such as methanol that is supplied to first
anode electrode 64A and second electrolyte 65B, unreacted methanol and
carbon dioxide that are generated after the reaction, and the like can be
reliably prevented from leaking through the contact surfaces between
anode-side end plate 40 and first electrolyte 64B and between the
separator and second electrolyte 65B. Further, displacement associated
with transformation of elastic body due to pressing force can be
prevented by the substrate.

[0087] Meanwhile, as described with reference to FIGS. 8A to 8D, the upper
surfaces of the grooved shapes in the vicinities of inlets 54, 83 and
outlets 56, 84 of gas flow channels 52, 82 formed on separator 80 and
cathode-side end plate 50 are crossed over and sealed by first substrate
72 of first sealing member 70 and second substrate 76 of second sealing
member 75. At this time, with the mechanical strength of first substrate
72 and second substrate 76 being sufficiently larger than the pressing
force generated at the time of stacking of the fuel cell stack,
transformation of first substrate 72 toward the inside of the groove on
gas flow channel 82 and transformation of second substrate 76 toward the
inside of the groove on gas flow channel 52 by the pressing force are
suppressed. It is thus possible to uniformly ensure cross-sectional areas
of the respective gas flow channels and the respective inlets and outlets
which are formed by the respective substrates and the gas flow channels.
Moreover, since the pressing force to compress first electrolyte 64B and
second electrolyte 65B through first elastic body 74 and second elastic
body 78 of first sealing member 70 and second sealing member 75 do not
decrease even on the grooves, it is possible to prevent deterioration in
sealing performance.

[0088] According to Embodiment 2, also in the fuel cell stack with two
membrane electrode assemblies stacked with the separator interposed
therebetween, it is possible to realize a reliable sealing structure with
a simple configuration to compress and press first electrolyte 64B and
second electrolyte 65B from one sides thereof through first sealing
member 70 and second sealing member 75.

[0089] Moreover, according to Embodiment 2, similarly to Embodiment 1,
each sealing member is made up of the substrate with high shape
stability, thereby making it unnecessary to form the sealing structure
integrally with cathode-side end plate 50 or separator 80. Consequently,
since the fuel cell stack can be formed by stacking, while mounting, each
constitutional element and then fastening the stacked elements, even when
the constitutional element becomes defective after the assembly, it is
possible to replace the element with ease, so as to produce a fuel cell
stack with high productivity and low cost.

Embodiment 3

[0090] A fuel cell stack in Embodiment 3 of the present invention is
described hereinafter with reference to FIG. 11.

[0091]FIG. 11 is a sectional view explaining a structure of a fuel cell
stack in Embodiment 3 of the present invention. Fuel cell stack 90 of
Embodiment 3 is different from fuel cell stack 60 of Embodiment 2 in that
three membrane electrode assemblies are provided and one membrane
electrode assembly is stacked between two separators having a fuel flow
channel and a gas flow channel. A description is given hereinafter with a
focus on constitutional elements different from those of fuel cell stack
60 of Embodiment 2.

[0092] Specifically, as shown in FIG. 11, third membrane electrode
assembly 94, third sealing member 100 that realizes the sealing
structure, and separator 110 are inserted in between separator 80 and
second anode electrode 65A of second membrane electrode assembly 65 of
fuel cell stack 60 of Embodiment 2, stacked with anode-side end plate 40
and cathode-side end plate 50 interposed therebetween, and integrated
through a fastening member not shown in the figure, to constitute fuel
cell stack 90 of the present embodiment.

[0093] Herein, as with membrane electrode assembly 24 of Embodiment 1
shown in FIGS. 4A and 4B, third electrolyte member 94B is sandwiched
between third anode electrode 94A and third cathode electrode 94C, to
constitute the third membrane electrode assembly 94. Third protruding
section 94D is provided which is exposed from the peripheries of third
electrolyte member 94B, third anode electrode 94A and third cathode
electrode 94C.

[0094] Further, as with sealing member 30 of Embodiment 1 shown in FIGS.
5A and 5B, third sealing member 100 is at least made up of ringed third
substrate 102 provided with an opening larger than the periphery of the
third anode electrode or the third cathode electrode, and third elastic
body 104 formed on one surface of third substrate 102 and at least in
contact with third protruding section 94D of third electrolyte member 94B
in third membrane electrode assembly 94. Therefore, third substrate 102
is structured so as to make third anode electrode 94A and third cathode
electrode 94C present inside.

[0095] As with separator 80 of Embodiment 2 which is shown in FIGS. 10A to
10D, separator 110, provided between third cathode electrode 94C in third
membrane electrode assembly 94 and second anode electrode 65A in second
membrane electrode assembly 65, has grooved gas flow channel 112 on one
surface, and grooved fuel flow channel 115 on the other surface.

[0096] As shown in FIG. 11, by stacking of each of the constitutional
elements described above, third elastic body 104 of third sealing member
100 comes into contact with the surface of separator 80 which is formed
with fuel flow channel 85 with third protruding section 94D of third
electrolyte member 94B in third membrane electrode assembly 94 interposed
therebetween. Further, third substrate 102 of third sealing member 100
comes into contact with the surface of separator 110 which is formed with
gas flow channel 112. The surface of separator 110 which is formed with
fuel flow channel 115 is opposed to second anode electrode 65A in second
membrane electrode assembly 65. Moreover, second elastic body 78 of
second sealing member 75 comes into contact with the surface of separator
110 which is formed with fuel flow channel 115 with second protruding
section 65D of second electrolyte 65B interposed therebetween. Other
configurations are similar to those of Embodiment 2, and descriptions
thereof are omitted.

[0097] Fuel cell stack 90 is formed in the above manner. At this time,
similarly to the first sealing member and the second sealing member,
third elastic body 104 in convex shape is formed on third substrate 102
as third sealing member 100. For this reason, an area of third elastic
body 104 which is in contact with third electrolyte member 94B is smaller
than an area of third elastic body 104 which is in contact with third
substrate 102. This leads to compression of third electrolyte member 94B
by large pressing force of third sealing member 100, thus allowing
hermetic sealing with high sealing surface pressure.

[0098] Accordingly, the fuel such as methanol that is supplied to third
anode electrode 94A, unreacted methanol and carbon dioxide that are
generated after the reaction, and the like can be reliably prevented from
leaking through the contact surface between separator 80 and third
electrolyte member 94B and the contact surface between separator 110 and
second electrolyte 65B. Further, displacement associated with
transformation of third elastic body 104 due to pressing force can be
prevented by third substrate 102.

[0099] Meanwhile, as described with reference to FIG. 8, the upper surface
of the groove shape in the vicinities of inlet 83 or outlet 84 of gas
flow channel 112 formed on separator 110 is crossed over and sealed by
third substrate 102 of third sealing member 100. At this time, with the
mechanical strength of third substrate 102 being sufficiently larger than
the pressing force generated at the time of stacking of the fuel cell
stack, transformation of third substrate 102 toward the inside of the
groove on the gas flow channel by the pressing force is suppressed. It is
thus possible to uniformly ensure cross-sectional areas of gas flow
channel 112, and inlet 83 and outlet 84 which are formed by third
substrate 102 and gas flow channel 112. Further, since the pressing force
to compress third electrolyte member 94B through third elastic body 104
of third sealing member 100 does not decrease even on the groove, it is
possible to prevent deterioration in sealing performance.

[0100] According to Embodiment 3, also in the fuel cell stack with three
membrane electrode assemblies stacked with the separators interposed
therebetween, similarly to the fuel cell stack of Embodiment 2, it is
possible to realize a reliable sealing structure with a simple
configuration to compress and press each electrolyte membrane from one
side thereof.

[0101] Moreover, according to the present embodiment, similarly to
Embodiment 2, each sealing member is made up of the substrate with high
shape stability, thereby making it unnecessary to form the sealing
structure integrally with the cathode-side end plate, the separator, or
the like. Consequently, since the fuel cell stack can be formed by
stacking, while mounting, each constitutional element and then fastening
the stacked elements, even when the constitutional element becomes
defective after the assembly, it is possible to replace the element with
ease, so as to produce a fuel cell stack with high productivity and low
cost.

[0102] It is to be noted that the description has been given by means of
the example of the three membrane electrode assemblies in Embodiment 3,
this is not restrictive. For example, a fuel cell stack stacked with
three or more membrane electrode assemblies with a plurality of
separators interposed therebetween may be formed. This can realize a fuel
cell stack with an arbitrary configuration such as parallel connection or
serial connection in accordance with a voltage, a current or power
required by external equipment.

[0103] Hereinafter, FIGS. 12A and 12B shows as an example fuel cell stack
150 having six membrane electrode assemblies. FIG. 12A is a perspective
view showing a structure of another example of a fuel cell in Embodiment
3 of the present invention, and FIG. 12B is a sectional view taken along
line 12B-12B of FIG. 12A.

[0104] As shown in FIGS. 12A and 12B, similarly to the fuel cell stack of
Embodiment 3, fuel cell stack 150 is made up of six membrane electrode
assemblies, five separators each provided among those assemblies, and an
anode-side end plate and a cathode-side end plate which vertically
sandwich those assemblies. At this time, anode-side backing plate 120 and
cathode-side backing plate 122 are provided according to the need for the
purpose of uniformly pressurizing and holding the fuel cell stack.
Herein, anode-side backing plate 120 and cathode-side backing plate 122
are made up, for example, of an insulating resin, a resin containing
ceramic or a glass fiber, a metal plate coated with an insulating film,
or the like. It is to be noted that anode-side backing plate and
cathode-side backing plate may also be applied to the above embodiments.

[0105] The description has been given in each of the above embodiments by
taking the DMFC as the example, but this is not restrictive, and the
configuration of the present invention is applicable to any fuel cell so
long as the fuel cell uses a similar power generating element to one used
in a fuel cell stack. For example, the configuration of the present
invention is applicable to a so-called polymer solid electrolyte fuel
cell, methanol reforming fuel cell and the like, which use hydrogen as a
fuel.

[0106] Further, the description has been given in each of the above
embodiments by basically taking as the example the fuel cell stack that
prevents leakage of the fuel and the gas and has excellent reliability,
but this is not restrictive. For example, as shown in FIG. 1, a fuel cell
may be at least made up of the fuel cell stack in each of the above
embodiments, the fuel supply section that supplies the anode electrode
with the fuel, and the oxidant supply section that supplies the cathode
electrode with the oxidant. This can realize a fuel cell excellent in
leakage resistance and further easy to assemble and replace, thus having
high reliability.

INDUSTRIAL APPLICABILITY

[0107] The fuel cell stack of the present invention and the fuel cell
using the same are useful as a power source of electronic equipment
especially required to have high reliability as well as a compact size
and portability.